This invention relates generally to media sheet feed mechanisms, and more particularly, to a media sheet pick and feed system which operates effectively regardless of media tray content and which enables easy re-loading of the media tray.
Print recording devices, such as printers, fax machines and copy machines, and print scanning devices often include an input media tray. A media sheet is picked from the input tray and fed along a media path to receive print recording or to undergo print scanning. One common mechanism for picking and feeding a media sheet employs a D-shaped wheel. During rotation of the wheel the curved portion contacts and picks a media sheet. Subsequent to the pick action the flat portion of the D-shaped wheel is adjacent to the picked media sheet, but out of contact with the media sheet. The media sheet is fed from the media tray while the flat portion of the wheel is adjacent but out of contact with the media sheet.
Another known pick mechanism includes a drive gear mounted on a shaft which in turn is coupled to a drive motor. The drive motor turns the shaft and drive gear during a pick operation. The drive gear engages a driven gear to which is rigidly connected a pick roller. Thus, the drive motor rotates the pick roller. The pick mechanism is moved into and out of contact with a media sheet to be picked by the rotation of the drive gear. When the drive gear rotates in one direction the driven gear and pick roller move into contact with a media sheet. Continued rotation in such direction causes the media sheet to be picked and moved onto a media feed path. Typically, rotation in the opposite direction causes the drive gear and pick roller to move out of contact with the media sheet. A shortcoming of this mechanism is that a spring-loaded tray is needed to bias the media sheets toward the pick range of the pick roller. Further, the media tray needs to be removed during reloading (or alternatively a mechanism is needed during reloading to depress the spring-loading plate which raises a media sheet into the pick range).
In U.S. Pat. No. 5,547,181 issued Aug. 20, 1996 to Underwood for xe2x80x9cMedia Sheet Pick and Feed System,xe2x80x9d Underwood discloses a clutch mechanism which allows the pick roller to remain in contact with the media sheet as the media sheet continues out of the media tray along the feed path. In particular, the clutch disengages the drive gear from the drive motor allowing the pick roller (along with the drive gear and driven gear) to xe2x80x9cfreexe2x80x9d wheel. This approach eliminates the need for a spring-loaded media tray.
According to the invention, a pick mechanism includes a hinged pick arm which moves between a retracted position and a varying, operative position. The pick arm includes a pick roller toward one end in the direction of a media sheet. The pick arm is anchored about a pivot axis toward another end. The pick arm is hinged along its length at a hinge point between the two ends. In various embodiments a drive motor is coupled, either directly or through a transmission, to the pick roller to rotate the pick roller.
According to another aspect of this invention, when the pick arm is in the retracted position, the pick arm is spring-biased to be at a first orientation about the hinge point (e.g., straight). An advantage of this is that the pick roller is biased away from the media stack allowing a media tray to be extracted without interferencexe2x80x94such as when being extracted to replace media sheets.
According to one aspect of the invention, as the pick arm is moved from the retracted position, the pick roller makes contact with a media sheet. As the drive motor rotates the pick roller, the friction between the pick roller and the media sheet causes a torque about the hinge point causing the pick arm to hinge. As the pick arm hinges from the first orientation into another orientation the pick roller stays in an operative position to pick a media sheet. While the pick arm is in an operative position, the rotating pick roller applies a force to pick a media sheet from a media stack and move the media sheet toward a separation ramp. The separation ramp isolates the pick forces to act upon the top media sheet, which is moved onto a media path where a feed roller captures a leading edge. The feed roller then continues to pull the remaining portion, if any, out of the media tray and along the media path where a recording or scanning operation may occur.
According to another aspect of this invention, the pick arm has a proximal portion extending at least from the pivot point to the hinge point and a distal portion extending at least from the hinge point to the pick roller. As the pick arm hinges, the proximal portion rotates about the pivot point until reaching a first mechanical stop. Concurrently the distal portion rotates about the hinge point. The angle that the distal portion makes relative to the proximal portion is referred to as angle xcex1.
Another angle of interest while the pick arm is in an operative position is the angle xcex2 which the distal portion forms relative to the length of the media sheet. The proximal portion may or may not be parallel to the media sheet while the pick arm is in an operative position. Thus, angle xcex2 need not be the same as angle xcex1. As either of angle xcex1 and angle xcex2 increases, the normal force acting on the pick roller increases at the expense of a normal force acting on the pivot point of the pick arm. An advantage of increasing the normal force acting on the pick roller is that heavier media sheets are picked with more reliability.
Increases in either of angle xcex1 or angle xcex2, however, translate the pick roller away from the media separation ramp. Such translation increases the potential for media sheet buckling. Accordingly, there is a trade-off between minimizing pick roller translation and maximizing angles. The angle stop mechanism limits angle xcex1 to a maximum angle so os to limit translation of the pick roller. In an alternative embodiment an angle stop mechanism instead or in addition limits angle xcex2 to a maximum angle so as to limit translation of the pick roller.
According to one advantage of this invention, media sheets of varying weights are effectively picked from a media sheet stack. These and other aspects and advantages of the invention will be better understood by reference to the following detailed description taken in conjunction with the accompanying drawings.